Since the benefits of mammography screening are uncertain for women >75 years and there are important harms, guidelines recommend that primary care providers (PCPs) engage women >75 years in shared decision making (SDM). The challenge is in weighing the trade-off between potentially finding a breast cancer early which may in turn help an older woman live longer and/or better, or instead result in her being harmed by work-up and/or treatment of a breast cancer that never otherwise would have caused problems in her lifetime (overdiagnosis). Ideally, screening decisions should consider an older woman's breast cancer risk, health, and preferences. However, 56% of women >75 years are routinely screened, including many with short life expectancy, and few are informed of the harms. In prior work we found that older women want to talk about these decisions with their PCPs. However, PCPs feel ill-prepared and unsupported to engage older women in SDM and request an easy to use and flexible web-based tool (i.e., a conversation aid) that could provide personalized information on the benefits and harms of mammography screening based on each patient's own breast cancer risk and health. Conversation aids (CAs) are increasingly used and are designed to be brief, require minimal training, fit into clinical work flow, and facilitate SDM. They have been shown to improve SDM and to increase satisfaction; however, despite the need, no CA exists to support SDM around mammography screening between PCPs and older women. Therefore, we, an interdisciplinary team of PCPs, experts in SDM and implementation science, modeling researchers from the NCI-funded Cancer Intervention and Surveillance Network (CISNET), and other expert stakeholders, aim to develop and test an interactive web-based conversation aid (CA) on mammography screening for PCPs to use with women >75 years, and involved family members during a visit. In Aim 1, we will leverage two CISNET models to estimate the personalized benefits and harms of mammography screening in women >75 years based on age, race, comorbidity, and breast cancer risk, necessary for decision-making. Model generated outcomes will be used to populate the CA which we will develop and revise in Aim 2 using an established iterative end-user centered approach that includes observing use of the CA by 10 PCPs practicing in diverse settings during 30 clinical encounters. Once we have developed a CA that supports SDM, we will pilot test the CA in a pretest-posttest trial including 40 PCPs from Boston-area community, academic, and safety-net practices, 100 women >75 years and 25 of their family members, and 10 medical assistants. The goal of the pilot study is to show that the CA is feasible to use during primary care visits in diverse settings and to obtain pilot data on the CA's effects to inform implementation and a future pragmatic trial. We hypothesize that our novel CA will increase PCP self-efficacy to engage older women in SDM and as a result older, women will make more informed, value-concordant screening decisions thereby maximizing the benefits of screening while minimizing its harms.